Also amusing that Casey, the lawyer, doesn't understand what circumstantial evidence is. "Circumstantial" is not synonymous with "weak." Cases can, and very often are, proven beyond a reasonable doubt through circumstantial evidence. It's basically any evidence other than witness testimony.

E.g., the bloody knife with the defendant's fingerprints on it is circumstantial evidence that he stabbed the victim. It may not prove the case in itself ("a brick is not a wall"), but you add enough similar circumstantial evidence to the mix and you manage to convince the jury. This is basic law-school stuff.

If we're talking about piecing together the evolution of a species, such as humans, in the distant past, I don't see how you could have anything but circumstantial evidence.